Question

3. The sum of first 9 terms of an arithmetic sequence
is 45 and the sum of first 18 terms is 171
a) What is the sum of its 10th to 18th terms?
b) What is its 5th term ?
c) Find its 14th term
d) Find the sum of 5th to 14th terms​

Answer 1

Answer:

To find the sum for arithmetic sequence, sn= n(n+1)/2, it is shown (n+1)/2, can be replaced with the average of nth term and first term.

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Answer 2

Answer:

A) 126

B) 25

C)101

Step-by-step explanation:

A)sum of its 10th to 18th term=sum of first 18th term - sum of first 10th term

=171-45=126

B)5th term is 25

C)14th term is 101 (by an=a1+(n-1)d

D)sum of 5th to 14th term=25+101=126